Tire Ruler255/45R20 dimensions
| Overall diameter (height) | 29.04″ · 737 mm |
| Section width | 10.04″ · 255 mm |
| Sidewall height | 4.52″ · 115 mm |
| Wheel diameter | 20″ |
| Rim width (rule of thumb) | 7–9″ |
| Circumference | 91.2″ |
| Revolutions per mile | 695 |
| In inches (flotation style) | 29.0 × 10.0R20 |
How it’s calculated: the sidewall is 45% of the 255 mm width = 114.8 mm (4.52″). Add two sidewalls to the 20″ wheel: 20 + 2 × 4.52 = 29.04″.
Bigger tires than 255/45R20 on 20″ wheels
| Size | Height | Taller by | 60 mph reads |
|---|---|---|---|
| 265/45R20 | 29.4″ | +0.35″ (+1.2%) | 60.7 mph |
| 245/50R20 | 29.6″ | +0.61″ (+2.1%) | 61.3 mph |
| 275/45R20 | 29.7″ | +0.71″ (+2.4%) | 61.5 mph |
| 255/50R20 | 30.0″ | +1.00″ (+3.5%) | 62.1 mph |
| 265/50R20 | 30.4″ | +1.40″ (+4.8%) | 62.9 mph |
“60 mph reads” is your real speed when a speedometer set up for 255/45R20 shows 60. Above about 3% taller, most trucks need a leveling kit or lift, and the speedometer should be recalibrated.
Sizes equivalent to 255/45R20
Within 1.5% of the same height on a 20″ wheel. Usually interchangeable for the speedometer; check width, load index and clearance.
| Size | Height | Width | Difference |
|---|---|---|---|
| 245/45R20 | 28.7″ | 9.6″ | −1.2% |
| 265/45R20 | 29.4″ | 10.4″ | +1.2% |
| 275/40R20 | 28.7″ | 10.8″ | −1.3% |
Same height on a different wheel size
Changing wheel size (plus or minus sizing) while keeping the overall height keeps your speedometer right:
- 235/75R15: 28.9″ tall on a 15″ wheel (−0.5%)
- 225/75R16: 29.3″ tall on a 16″ wheel (+0.9%)
- 235/70R16: 29.0″ tall on a 16″ wheel (−0.3%)
- 235/65R17: 29.0″ tall on a 17″ wheel (−0.0%)
- 235/60R18: 29.1″ tall on an 18″ wheel (+0.2%)
- 225/60R18: 28.6″ tall on an 18″ wheel (−1.4%)
- 255/55R18: 29.0″ tall on an 18″ wheel (+0.0%)
- 235/55R19: 29.2″ tall on a 19″ wheel (+0.5%)
- 255/50R19: 29.0″ tall on a 19″ wheel (+0.0%)
Frequently asked questions
Is 255/45R20 a 29 inch tire?
Yes. 255/45R20 is 29.04 inches tall, so it's sold and talked about as a 29-inch tire.
What size is 255/45R20 in inches?
255/45R20 is 29.0 inches tall (overall diameter), 10.0 inches wide, with a 4.5 inch sidewall, and fits a 20 inch wheel.
What tire size is equivalent to 255/45R20?
Sizes within 1.5% of the same diameter on a 20" wheel: 245/45R20 (28.7"), 265/45R20 (29.4"), 275/40R20 (28.7"). Check load index and width before swapping.
What rim width fits 255/45R20?
As a rule of thumb, about 7–9 inches. The tire maker's spec sheet lists the approved range for each model.
How many revolutions per mile does 255/45R20 make?
About 695 revolutions per mile in theory (circumference 91.2 in). Real tires turn slightly more because they flatten under load.